1. Field of the Invention
The invention relates to an exhaust gas control apparatus for an internal combustion engine, in which a flow passage for exhaust gas is switched between a passage in which an HC adsorption portion is provided, and a passage that bypasses the HC adsorption portion, to purify the exhaust gas, and a method of controlling the same.
2. Description of the Related Art
An apparatus that executes a control to switch a flow passage for exhaust gas using a switching valve is available. The apparatus executes the control so that the exhaust gas flows in a passage in which an HC adsorption portion (HC adsorption tube) is provided, or a passage that bypasses the HC adsorption portion. The HC adsorption portion adsorbs HC (hydrocarbon) in the exhaust gas. For example, Japanese Patent Application Publication No. 8-165920 (JP-A-8-165920) describes an exhaust gas control apparatus in which a flow passage for exhaust gas is switched between a flow passage in which an HC adsorption portion is provided, and an exhaust passage provided in parallel with the flow passage in which the HC adsorption portion is provided, using a negative pressure. In the exhaust gas control apparatus, when an engine is cold after the engine starts, the exhaust gas is directed to flow in the flow passage in which the HC adsorption portion is provided.
As a technology for ensuring the startability of an engine when the engine is cold, the following technology is available. Japanese Patent Application Publication No. 2001-65375 (JP-A-2001-65375) describes the technology in which, in an internal combustion engine for a hybrid system, when the engine is cold, the amount of intake air is increased by advancing the opening timing of an intake valve so that an increase in generated torque is promoted, and the startability is improved.
However, in the technology described in the publication No. 8-165920, when the engine is cold, an appropriate negative pressure is not obtained, and the switching valve does not completely close the exhaust passage in which the HC adsorption portion is not provided. Therefore, there is a possibility that HC may be discharged. In the technology described in the publication No. 2001-65375 as well, when the engine is cold, it is not possible to reliably generate the negative pressure required for making the switching valve completely close the exhaust passage in which the HC adsorption portion is not provided.